In general, the various working sections of an agricultural combine may be said to include a forwardly-positioned header section which carries a cutterbar for harvesting the crop, a platform for supporting the harvested crop, a reel above the platform for raking the crop toward the cutterbar and platform, and an auger associated with the platform for combining and feeding the harvested crop on the platform rearwardly; an intermediate feeder section for conveying the crop rearwardly from the header to a threshing section; and a thresher in the threshing section for separating the main edible crop from the remaining plant parts. For efficient harvesting of low-growing crops, it is, of course, desirable to position the cutterbar as close to the ground as possible without jamming or digging into the soil.
It is well-known to provide floating or flexible cutterbars for the harvesting of low-growing crops. Such floating cutterbars are able to flex vertically to compensate for irregularities in the ground surface, while the header itself remains comparatively rigid and fixed so that the crop can be efficiently cut close to the ground. However, in order to stabilize such cutterbars and avoid damage thereto, it became necessary to apply a counterbalancing, upwardly directed force to the cutterbars.
Representative of the efforts made to supply the counterbalancing force is U.S. Pat. No. 4,091,602, which discloses a plurality of tapered leaf springs rigidly connected between the main frame of the header and the cutterbar. Those springs were upwardly bowed, and telescoping stabilizer bars were provided to prevent damage or buckling of the springs. The counterbalancing force exerted on the cutterbar was a fixed function of the spring structure and there was no means provided for adjusting that force.
U.S. Pat. No. 4,414,793 illustrates another effort to provide a counterbalancing force for a flexible cutterbar. In that structure, a plurality of upwardly bowed leaf springs are connected between an intermediate transverse bar on the header and the cutterbar. While the rearward connection to the transverse bar was rigid, the forward end of the spring made only a sliding contact with the bottom surface of the cutterbar. According to the patent's teachings, the counterbalancing force on the cutterbar could be varied by attaching a greater number of leaf springs or by stacking one spring atop another at a given point of connection. In addition to requiring additional springs, the described means for adjusting the counterbalancing force was cumbersome and imprecise at best.
There thus exists a need for a counterbalancing support for the flexible cutterbars of combines which is readily adjustable as required to compensate for varying conditions of ground surface, nature of crop, and load applied to the header.